1. Field of the Invention
The present invention relates to a lighting apparatus using microwave, and particularly, to a lighting apparatus using microwave including a dielectric mirror reflecting a light generated in a bulb forward.
2. Description of the Background Art
Generally, a lighting apparatus using microwave is an apparatus for emitting a visible ray or ultraviolet rays by radiating a microwave to an electrodeless plasma bulb, and it has longer life span than that of an incandescent lamp or of a fluorescent lamp and has superior lighting effect.
FIG. 1 is a longitudinal cross-sectional view showing an example of a lighting apparatus using microwave according to the conventional art.
As shown therein, the lighting apparatus using the microwave according to the conventional art comprises: a magnetron 2 installed inside a case 1 for generating microwave; a high voltage generator 3 for raising utility AC power into high voltage and providing the magnetron with the power; a waveguide 4 for transmitting the microwave generated in the magnetron 2; a mesh screen 6 installed on an outlet portion of the waveguide 4 for breaking a leakage of the microwave and passing the light; and a bulb 5 located in the mesh screen 6 for emitting light as a material filled in the bulb 5 becomes plasma by the microwave energy transmitted through the waveguide 4.
The lighting apparatus using the microwave includes a reflector 7 disposed in front of the case 1 which is a peripheral area of the mesh screen 6 for reflecting the light generated in the bulb 5 forward concentratively.
Also, a dielectric mirror 8 passing the microwave transmitted through the waveguide 4 and reflecting the light emitted from the bulb 5 forward is installed in an outlet portion 4a of the waveguide 4.
Herein, the reflector 7 is formed as a curved surface of parabola shape, however, the dielectric mirror 8 is formed as a plane having a hole 8a on a central part so as to penetrate a shaft portion 5b of the bulb 5.
On the other hand, a cooling fan assembly 9 for cooling down the magnetron 2 and the high voltage generator 3 is disposed on rear area of the case 1. In addition, unexplained reference numeral 9a represents a fan housing, 9b represents a blast fan, M1 represents a bulb motor, and M2 represents a fan motor.
An operation of the lighting apparatus using the microwave according to the conventional art will be described as follows.
When an operation signal is inputted to the high voltage generator 3, the high voltage generator 3 raises AC power and provides the magnetron 2 with the raised high voltage. And the magnetron 2 is oscillated by the high voltage and generates microwave of very high frequency. The generated microwave is radiated into the mesh screen 6 through the waveguide 4 to emit light having its own emission spectrum by discharging the material filled in the bulb 5. In addition, the light is reflected by the reflector 7 and by the dielectric mirror 8 forward.
However, according to the conventional lighting apparatus using the microwave described above, the light reflected by the reflector 7 is radiated as a straight light and concentrated, but the light reflected by the dielectric mirror 8 is dispersed to a plurality of directions according to incidence angles, as shown in FIG. 2. Therefore, some of the light emitted from the bulb 5 is reflected on the dielectric mirror 8 and lost, and thereby the lighting effect is lowered.
Also, the bulb 5 should be disposed on a focal point of the reflector 7 in order to generate straight line light most, however, the dielectric mirror 8 formed as a plane is installed nearly to the focal point. Therefore, it is difficult to dispose the bulb 5 exactly on the focal point of the reflector 7.